The present invention relates generally to electrically conductive fiber filled polymer composites characterized by improved line or point-to-point conductivity and enhanced electromagnetic interference shielding effectiveness.
In today""s electronic age and particularly as a result of advances in digital technologies, electrical malfunctions resulting from electromagnetic interference (EMI) have been proliferating. Recently, ever-increasing numbers of cordless and cellular phone users have compounded the problem. As a result, interference with television and telephone reception, and the proper operation of various instruments such as flight instruments in an airplane as well as the inadvertent activation of electrically controlled devices such as garage door openers now commonly occur.
In an effort to address this problem, manufacturers are seeking ways to provide finished parts with improved EMI shielding characteristics. Toward this end it is known to utilize metal paint application (e.g., silver, copper, nickel), cathode sputtering, foil application, vacuum metalizing, electroplating, flame/arc spraying and graphite paint application. While useful, these techniques generally suffer from one or more drawbacks including but not limited to high processing costs and a limited service life due to chipping, cracking and/or peeling of the surface treatment.
Electrically conductive fiber-filled polymer composites generally avoid these problems. Specifically, the composites are typically molded to provide a housing, cover or shroud providing desired EMI shielding characteristics. Unfortunately, due to the thin layer of polymer on the surface of the molded parts or the occasional presence of resin rich areas/spots on the surface thereof line or point-to-point surface contact resistance is usually very high. For many applications in the electronic industry, the line or point-to-point contact resistance must be very low in order to form a complete electrically conductive path and to be EMI shielding effective. Thus, a need is identified for improving the line or point-to-point contact resistance on the surface of a conductive fiber filled polymer composite.
In accordance with the purposes of the present invention as described herein, a method is provided for improving the line or point-to-point surface contact resistance of an electrically conductive fiber filled polymer composite. The method includes evaporating a thin polymer layer on a surface of the conductive fiber filled polymer composite and exposing an electrically conductive fiber network underneath. The evaporating may be performed by using a laser.
The method may also be described as using a laser with a laser power level of between about 3 to about 150 watts to evaporate a thin polymer layer on a surface of the conductive fiber filled polymer composite to a depth of between about 1 to about 250 microns and exposing an electrically conductive fiber network.
The method may be further described as including the step of moving the laser at a laser head speed of between about 1 to about 500 inches/second across the surface of the composite. Thus, the method includes the etching of a pattern across the surface of the electrically conductive fiber filled polymer composite.
In accordance with yet another aspect of the present invention, an EMI shielding apparatus is provided comprising an electrically conductive fiber filled polymer composite having an etched surface exposing an electrically conductive fiber filled network underneath. The etching is to a depth of between about 1 to about 250 microns.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.